Temperature clamping method for anti-contamination and collimating devices for thin film processes

ABSTRACT

In a thin film process system, an anti-contamination device, anti-flake shield or collimator plate, is fit to a process chamber. By maintaining a temperature differential between the chamber body and the device, or between the device and any adapter used to conform the device to the chamber apparatus, the device expands to maintain a substantially sealing press fit to the chamber body. The temperature differential can be maintained even when the process is finished until it is time to remove the device for cleaning or disposal and replacement.

This is a continuation of application Ser. No. 08/198,920 filed Feb. 18,1994, now U.S. Pat. No. 5,419,029.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to thin film technology and,more particularly, to anti-contamination shields and collimators forthin film process apparatus.

2. Description of the Related Art

In thin film deposition and etch processes, such as physical vapordeposition ("PVD"), II or sputtering, a target material is bombarded byhigh energy gaseous ions. Material from the target is dislodged andsputters onto a work piece. The work piece may be, as examples, asemiconductor wafer, a magnetic disk, or a flat panel display.

For example, a PVD chamber, such as shown in FIGS. 1A and 1B (Prior Art)usually includes a chamber apparatus 14 generally constructed ofstainless steel. A shield 19, generally constructed of aluminum, ismounted to the chamber directly or through use of an adapter 17 (alsoconstructed of stainless steel) is sometimes, fitted appropriately toconform the chamber cavity. A clamping ring 16 is also sometimesemployed in such apparatus.

The shield 19 is of an appropriate size and shape to protect the chambercavity. For example, during the course of thin film processing, a workpiece 36, such as a semiconductor wafer, is placed within the PVDchamber 14 through an opening 31 by automated machinery. A wafer table25 is raised into a target location through the shield 19 to a positionwhere PVD processing occurs. As a DC-biased target 30 on source 20(electrically isolated by insulator 28) is bombarded by ions (such asargon) generated by a plasma created between the DC-biased target 30 andthe work piece 36, target atoms are ejected within the chamber 14 andonto the work piece 36. The shield 19 prevents excess materialsputtering from the target 30 from contaminating the remainder of thePVD chamber interior. Substantial heat is generated during this process,raising the temperature of the shield 19 and the chamber apparatus 14.The shield 19 is replaced once the build-up of excess target materialreaches a point where flaking may impair further PVD processes.

Note that prior art type shields generally do not fully contact thechamber walls or adapter 17 during work piece processing. The shield 19can be bolted to an adapter 17. FIG. 2 (Prior Art) shows the typicalcomponents of the shield 19 and adapter 17 subsystem and mounting bolts21 that affix the shield 19 to the adapter 17. This procedure does notprovide a good thermal coupling between the shield 19 and the adapter 17or the chamber walls. During high power thin film processes (forexample, aluminum or collimated titanium-nitride deposition), the shieldmay reach temperatures as high as 300 to 500 degrees Centigrade. Thethermal expansion of the shield material can cause buckling or warpingof the shield 19. In such buckled or warped regions, the shield 19 losescontact with the adapter 17 or the inner chamber walls, deterioratingeven further the already poor thermal coupling. Excessive thermalexpansion may contribute to the harmful contamination of the work piece36.

Other shield mounting techniques, such as brazing or welding couldprovide good thermal contact, but are impractical within production PVDsystems as they make removal and replacement difficult.

Forced temperature maintenance, such as by water cooling the shieldduring high temperature processes, not only increases the complexity andcost of the system, but also risks the introduction of water vapor intothe PVD chamber which is highly destructive to the PVD process itself.

There is a need, therefore, for an improved mounting of ananti-contamination shield for thin film process systems. As will bedisclosed with respect to an alternative embodiment, the same principlesapply to collimator plates used in collimated PVD processes. The sameinventive principles can apply to any deposition and etch system whereshielding is used to protect chamber walls from deposited or etchedmaterial and where significant heat has to be removed from the activeinner portion of the chamber.

SUMMARY OF THE INVENTION

In accordance with the preferred embodiment of the present invention, amethod and resulting apparatus for mounting a removable shield in a thinfilm process system, having a thin film process chamber, is presented.The method includes inserting a shield having at least one Outer wallwith external circumferential dimensions less than the circumferentialdimensions of adjacent and complementary inner walls of the chamber, or,if used, an adapter for fitting a shield to a chamber apparatus. Thetemperature of the chamber is maintained such that the shield expandsmore than said chamber walls during operation of the thin film process.Thermal expansion of said shield compresses outer walls of the shield toinner walls of the chamber (or the adapter). The temperature differencebetween the chamber and the shield is maintained until it is desired ornecessary to remove the shield. With appropriate predetermined designfeatures, the press fit provides substantial thermal coupling betweenthe shield and the chamber, or adapter, inner walls.

It is an advantage of the present invention that it provides goodthermal contact-between a thin film process system shield and theprocess chamber.

It is another advantage of the present invention that it reducescontamination of a thin film process chamber.

It is another advantage of the present invention that it eliminates thenecessity for fastening mechanisms between the shield and adapter orprocess chamber body.

It is still another advantage of the present invention that the shieldtemperature and associated thermal expansion can be kept relatively low.

It is yet another advantage of the present invention that it can beapplied to collimator plates and other thin film deposition and etchsystems which employ anticontamination devices.

Other objects, features and advantages of the present invention willbecome apparent upon consideration of the following detailed descriptionand the accompanying drawings, in which like reference designationsrepresent like features throughout the FIGURES.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A (Prior Art) is an exploded, perspective view of a PVD chamberbody, an adapter and shield subsystem, and a clamping ring.

FIG. 1B (Prior Art) is a simplified, schematic, cross-sectional diagramof the PVD chamber of FIG. 1A, further depicting process devices inplace.

FIG. 2 (Prior Art) is an exploded, perspective view of an adapter andshield subsystem as shown in FIG. 1.

FIG. 3 is a simplified, schematic, cross-sectional diagram of a PVDsystem in accordance with the present invention.

FIG. 4 is a simplified, schematic, cross-sectional diagram of a PVDsystem as shown in FIG. 3 after implementation of the method of thepresent invention.

FIG. 5 is a simplified, schematic, partial cross-sectional diagram of analternative embodiment of a PVD system implemented in accordance withthe present invention.

The drawings referred to in this description should be understood as notbeing drawn to scale except if specifically noted.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made now in detail to a specific embodiment of the presentinvention, which illustrates the best mode presently contemplated by theinventor for practicing the invention. Alternative embodiments are alsobriefly described as applicable. The invention is disclosed in anexemplary embodiment for a PVD process chamber, but it will berecognized by those skilled in the art that the method and apparatusdisclosed is readily adaptable to other apparatus in the field of thinfilm process technology.

Referring now to FIG. 3, a generally cylindrical shield 19, having awall portion 24', is designed to slip fit coaxially into a PVD chamberbody 14 when both are substantially at room temperature (or some similarpredetermined ambient temperature) such that a small gap (designated"a") separates an outer wall 24 of shield portion 24' from a chamberinner wall 26. A shielding portion 22 of the shield extends radiallyinward into the chamber cavity. A similar gap separates the shield outerwall 24 from any adapter 17 longitudinally interposed between thechamber 14 and a support portion 21 of the shield 19. As is known in theart, an electrical insulator 28 is mounted to the adapter 17 andseparates the PVD target 30 from the chamber body 14.

When power is applied to the sputtering target 30, the resultantdischarge will heat up the interior of the chamber apparatus 14. Thechamber body 14, and adapter 17, if any, are maintained at asubstantially constant temperature (for example, by known water coolingtechniques applied to the outer walls of the PVD chamber, directly tothe PVD chamber, or to the adapter). Thus, the chamber apparatus remainssubstantially at a predetermined ambient temperature. The shield 19 willexpand. The materials chosen for the parts and the design tolerance ofgap "a" between the shield outer wall 24 and the chamber inner wall 26(or adapter 17, if used) is predetermined such that when the shield 19reaches a predetermined temperature, for example 100 to 200 degreesCentigrade, the shield 19 will have expanded so that the gap "a" isclosed and the shield outer wall 24 is firmly abutting the chamber innerwall 26 as shown in FIG. 4. The relatively large forces associated withthermal expansion will compress the shield 19 against the chamber innerwall 26, in a substantially sealing, thermally conductive, press fit. Ifan adapter 17 is employed, expansion to form a thermally coupledcompression fit between the adapter 17 and the shield 19 may besufficient so as to make contact with the chamber inner wall 26 anoptional requirement.

Once the PVD process is initiated, the temperature will tend to continueto rise until a high point is reached. However, the chamber inner wall26 (or adapter 17) being in compressive contact with the shield 19 formsa heat sink for the shield 19. In other words, the shield 19 temperaturewill be limited, or "clamped," to approximately the temperature at whichthe shield outer wall 24 is press fit to the chamber inner wall 26 (oradapter 17) and a steady state heat exchange is established. That is,the shield 19 will be substantially maintained at a temperature wherethermal coupling is such that heat flux out of the shield 19 into thechamber body 14 (or adapter 17) is equal to the heat flux into theshield 19 during the PVD process.

In the preferred embodiment, the chamber inner walls 26 and the shieldouter walls 24 are substantially cylindrical to ensure that the shield19 is pressed uniformly to the chamber walls 26 and to avoid anybuckling of the shield 19. While a cylindrical shape for the chamberwalls and shield has been demonstrated, it will be obvious to a personskilled in the art that other shapes in which the outer portion of theshield is complementary to the inner features of the chamber, or theadapter, to which it is to be heat clamped may be similarly designed.

In an exemplary embodiment, a stainless steel chamber body 14 (andadapter 17), having a cylindrical inner wall 26, is maintained atapproximately room temperature. The inner diameter of the chamber body14 is 15-inches. A cylindrical shield 19 can be fabricated from aluminummaterial having a room temperature, outer diameter of 14.96-inches. Suchtolerances can be easily met in the state of the art for manufacturingthe parts of such a system. Having a thermal expansion coefficient of25.10⁻⁶ K⁻¹, the shield 19 will expand to close the gap "a" and pressfit against the inner wall 26 (and/or adapter 17) at a temperature ofapproximately 120 degrees Centigrade. In other words, if the chamber ismaintained at room temperature, the shield 19 will be clamped to theinner wall 26 of the chamber body 14 at approximately 120 degreesCentigrade. It has been determined that a temperature differential rangeof fifty to three hundred degrees Centigrade is appropriate to maintainthermal coupling.

When the PVD process is finished, the DC-biasing is removed so that theheat load is eliminated while the work piece 36 is being extracted andthe table 25 reloaded. It is desirable to maintain the press fit sealbetween the shield 19 and the chamber body 14 (or adapter 17) until suchtime as the shield 19 is to be removed for cleaning or disposal. Asshown in FIG. 4, lamps, such as halogen or tungsten bulbs (as are knownto be used in pre-PVD processes to bake out water vapor from thechamber), may be employed to maintain the predetermined temperature atwhich the steady state heat flow was established, preventing contractionof the shield 19 after the processing cycle is finished.

Referring now to FIG. 5, an alternative embodiment of the invention isshown. This embodiment will be recognized by those skilled in the art asdisclosing a construction of special relevance for collimatedsputtering. A collimator plate 40 can be machined with such tolerancesthat it fits with a gap "a" into the PVD chamber at room temperature.Similar to the earlier described embodiments where the shieldtemperature is clamped during processing, the collimator 40 temperaturewill be clamped to that where the outer diameter of the collimatorequals the inner diameter of the PVD chamber. Note that clamping one ofthe gaps "a" or "b" or "c" achieves the goal of the present invention.

The foregoing description of the preferred embodiment of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in this art.Similarly, any thin film process steps described might beinterchangeable with other steps in order to achieve the same result.The embodiment was chosen and described in order to best explain theprinciples of the invention and its practical application to therebyenable others skilled in the art to understand the invention for variousembodiments and with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and theirequivalents.

What is claimed is:
 1. A method of inserting a shield into a thin filmprocessing chamber, said shield being of a size and of a material sothat it expands when heated during processing which comprisesa)inserting said shield into said chamber; and b) heating said shielduntil said shield contacts an inner portion of a wall of said chamber.2. A method according to claim 1 wherein the temperature of the shieldis maintained so that it retains its expanded condition until it isremoved from said chamber.
 3. A method according to claim 2 wherein saidshield temperature is maintained with a heating lamp.
 4. A methodaccording to claim 1 wherein the materials of said shield and saidchamber wall are thermally conductive.
 5. A method according to claim 4wherein the wall of said chamber is maintained at a preselectedtemperature lower than that of the shield during processing in thechamber, so that the wall acts as a heat sink for said shield duringprocessing.
 6. A method according to claim 5 wherein the temperaturedifference between the chamber wall and the shield is maintained atbetween about 50° and 300° C.
 7. A method according to claim 1 whereinsaid shield is maintained at all times it is within said chamber at atemperature so that it is in an expanded condition.
 8. A methodaccording to claim 1 wherein said chamber is a physical vapor depositionchamber.
 9. A method of inserting a collimator plate into a thin filmprocessing chamber, said collimator plate being of a size and of amaterial so that it expands when heated during processing whichcomprisesa) inserting said collimator plate into said chamber; and b)heating said collimator plate until said collimator plate contacts aninner portion of a wall of said chamber.
 10. A method of inserting ashield into a thin film processing chamber, said chamber including athermally conductive shield adaptor affixed to a wall of said chamber,said shield being of a size and of a material so that it expands whenheated during processing which comprisesa) inserting said shield intosaid chamber adjacent to said adaptor; and b) heating said shield untilsaid shield contacts said shield adaptor.